The first stone will be 10-in wide
The last stone will be 10-in wide
The stones in the middle will be alternating between 5-in and 10-in stones, making a total of 15-in
Total width = 145-in
Width after placing first and last stones = 145 - 20 = 125-in
Number of 15-in patterns incorporated in 125-in:
125/15 = 8.33
Therefore, he will place 8 10-inch stones within and 9 5-inch stones within the patter.
The total 10-inch stones used = 8 + 2 = 10